Mobile radio telephone system having an identity which can be dynamically changed

ABSTRACT

The invention relates to a mobile radio system having a plurality of mobile terminals (ME) connected with a mobile switching center (MZ) via an air interface for communication control and optionally for billing. The mobile terminals (ME) are controlled by a subscriber identity module (SIM) in which data for associating at least one user are stored, the subscriber identity module (SIM) having an identity (IMSI) associated therewith. For utilizing a mobile radio device for different purposes, such as private and business, a subscriber identity module is known which contains at least two permanently stored identities and thus has the disadvantage of being inflexible. The invention therefore proposes a subscriber identity module (SIM) containing a calculation rule for calculating from the stored identity (IMSI) at least one further identity (IMSI w ), the identities generated by the calculation rule being associated accordingly in the mobile switching center (MZ).

This application claims priority to the following applications (theentirety of all of which are incorporated herein by reference:PCT/EP99/03107 filed May 6, 1999.

BACKGROUND OF THE INVENTION

This invention relates to a mobile radio system having a plurality ofmobile terminals connected with a mobile switching center via an airinterface for communication control and optionally for billing. Inaddition the invention relates to a method for operating mobileterminals of a mobile radio system.

In known mobile radio systems, for example the GSM network, the mobileterminals are usually connected with a mobile switching center via anair interface. The mobile terminals are controlled by a subscriberidentity module. This subscriber identity module is usually designed inthe form of a chip card in ID-1 or ID-000 format disposed removably inthe mobile terminal. The subscriber identity module (SIM) is used interalia for granting the authorized person access to the mobile radionetwork and permitting call accounting. For this purpose the SIMcontains a subscriber identity (International Mobile Subscriber IdentityIMSI) for identifying the subscriber world-wide in all GSM networks. Thesubscriber identity usually has the billing account assigned theretothrough which call accounting is done.

In particular for double utilization of a mobile phone (e.g. forbusiness and private purposes) it has proven advantageous to equip thesubscriber identity module with at least one further identity. Europeanpatent specification EP 0 579 655 B1 discloses a method for mobiletelephone systems controlled by subscriber identity modules eachcontaining at least two alternatively usable identities. When beginningto operate the mobile unit the user can activate the desired identitythrough the insert direction of the subscriber identity module or byentering a personal identification number (PIN) via the keyboard.

The disadvantage of the known method is that the alternatively usableidentities must already be stored in the card upon its issue. That meansin practice that the number of alternatively usable identities mustalready be known when a mobile radio connection is applied for. Inparticular when a new identity is to be allotted later this can only bedone by issuing a new card, i.e. a new subscriber identity module.

The problem of the invention is therefore to state a mobile radio systemand a method for operating the mobile radio system and a subscriberidentity module which avoid the abovementioned disadvantages.

SUMMARY OF THE INVENTION

A mobile radio system is provided wherein the subscriber identity moduleused for controlling the mobile terminals contains a calculation rulefor calculating at least one further identity from the stored identity.Identities generated in accordance with the calculation rule areassociated accordingly in the mobile switching center. An alternativefor solving the abovementioned problem is to design the subscriberidentify module so as to permit generation of a request signal which istransmitted to the mobile switching center and processed there,whereupon an alternative identity is communicated to the subscriberidentity module via the air interface.

The advantage of the present invention is that one need not store allidentities on the chip card, i.e., the subscriber identity module. Thismakes the system more flexible to handle since the additional identitiescan be assigned after the card is issued to the user, i.e. after he hasapplied for the connection. It is thus possible for the owner of amobile phone having an associated identity to obtain a second identityat a later time without a new card having to be issued.

According to an advantageous development of the invention, thecalculation request for a new identity is triggered by the user by akeyboard entry or via the menu. In the simplest case one can provide inthe mobile phone a changeover switch having two or more switchingpositions each triggering an associated calculation process. Alternativemenu-driven triggering has the advantage that the menu display can becontrolled by the subscriber identity module so that no changes need bemade in the mobile terminal. This advantage also applies to a furtheradvantageous development of the invention by which the calculation orrequest for a new identity is initialized by entry of a PIN. In thiscase a plurality of personal identification numbers with which the useridentifies himself as authorized are stored in the subscriber identitymodule. Entry of a PIN then triggers not only the function enable butalso the calculation of the desired subscriber identity if the latterdoes not correspond to the original identity.

Since the mobile terminals of a mobile radio system are frequentlyoperated in outside networks, it has proven advantageous to calculate afurther directory entry (phone number) and/or a further authenticationkey together with the further identity. In particular the furtherdirectory entry has the advantage that the mobile terminal can only bereached with the corresponding phone number in the directory entry. Thispermits the user to ensure for example that he only gets private callsduring a private stay in the territory of an outside network. Thedifferent phone numbers for dialing the user also permit the costsassigned to the user that arise in the outside network to be assignedupon forwarding of a “business” call, i.e. a call to the phone numbernot currently selected.

The invention further relates to a method for operating mobile terminalswhich generates from a single identity stored in the subscriber identitymodule the further identities by a calculation rule if required. Themethod offers the advantage stated above for the mobile radio systemaccording to the invention that one need not store a plurality ofidentities in a card, but the system can work more flexibly since thecard can be issued without having to store all identities that mightpossibly be used.

According to the invention the calculation of the new identity can beperformed either in the subscriber identity module or in the mobileswitching center, in which latter case the mobile terminal sends arequest to the mobile switching center and the new identity iscommunicated to the mobile terminal and thus to the subscriber identitymodule via the air interface of the mobile radio system.

The inventive method provides for the further advantageous developmentthat the current identity is newly calculated for each identity for acheck, which is performed at the request of the mobile switching centeror the mobile terminal. In this way one need not provide any memoryspace for storing further identities in the subscriber identity module.

Should the current identity have to be available more quickly, forexample due to the calculation time necessary for calculation, it isalso possible to store the currently set identity temporarily in thesubscriber identity module.

The invention further proposes a subscriber identity module for a mobileterminal in a mobile radio system which is suitable for use by theabovementioned method. For this purpose a calculation rule is stored inthe subscriber identity module for calculating at least one furtheridentity from the stored identity. Alternatively, the subscriberidentity module can be designed to generate a request signal. In thiscase the subscriber identity module initializes calculation of the newidentity in the network center, so that calculation of the alternativeor further identity is not generated in the card, i.e. in the subscriberidentity module.

BRIEF DESCRIPTION OF THE DRAWINGS

Preferred embodiments of the invention will be explained more closely inthe following with reference to FIGS. 1 to 5, in which:

FIG. 1 shows the basic structure of a mobile radio network,

FIG. 2 shows the block diagram of a subscriber identity module,

FIG. 3 shows a first flow chart of the dynamic IMSI selection.

FIG. 4 shows a second flow chart of the dynamic IMSI selection, and

FIG. 5 shows an exemplary menu display.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 shows a mobile radio system consisting of mobile switching centerMZ, base station system BS and mobile station MS consisting of mobileterminal ME and subscriber identity module SIM. Subscriber identitymodule SIM is a chip card specific to mobile radio and yielding inconjunction with mobile terminal ME operable mobile station MS. Storedin the subscriber identity module are all data necessary for grantingnetwork access only to authorized persons and for performing callaccounting. The essential tasks of the subscriber identity module areauthentication vis-à-vis the mobile radio system and storage ofuser-specific data. In particular data concerning the identity of thesubscriber IMSI are stored in the subscriber identity module. Data andspeech are exchanged between mobile unit ME and base station BS by radiotransmission. Base stations BS are connected with mobile switchingcenter MZ. Mobile switching center MZ contains a visitor locationregister and a home location register in which user data are storedtemporarily (in the visitor location register) or permanently (in thehome location register). Important data are in particular thesubscribers' IMSI and the directory entries MSISDN associated with theIMSI. According to the invention, subscriber identity module SIMcontains one or more calculation rules RV for calculating from identityIMSI permanently stored there at least one further identity IMSI_(w). Inthe mobile switching center the further identities associated with anoriginal IMSI are stored or generated by the same calculation rule as inthe subscriber identity module.

FIG. 2 shows a rough block diagram of subscriber identity module SIM.This SIM contains arithmetic unit CPU connected with program memory ROM,working memory RAM and nonvolatile memory SP, preferably an E²PROM.Stored in nonvolatile memory SP are original identity IMSI andcalculating rule RV for calculating particular new identity IMSI_(w) atthe request of the user or at the request of the mobile terminal or themobile switching center. Calculating rule RV can also be storedalternatively in the ROM. The IMSI_(w) newly calculated by givencalculating rule RV can also be stored temporarily in working memory RAMso that it is immediately available at the request of the mobile radiosystem.

FIG. 3 shows an example of the flow chart for selecting a furtheridentity. In the figure the program start for IMSI selection isdesignated S1. The selection request is started either at the request ofthe user by a menu selection or at the request of the network or themobile unit. In program step S2 the user is asked for an entry or aprevious entry is accepted. In step S3 the selection entry from step S2is checked, and the corresponding calculating rule is executed accordingto step S41, S42, . . . S4 n. If the selected IMSI is the original IMSIno change is made or the value “0” is added to the original IMSI. Ifidentity 1 is selected a calculation is done by calculating rule RV1 andthe value “1” is added to the original IMSI. The same applies to allfurther possible identities up to IMSIn in step S4 n.

The newly calculated IMSL_(w) is then outputted in step S5. The IMSI_(w)outputted for authentication or a check is newly calculated at eachrequest of the mobile unit to subscriber identity module SIM, in whichcase the last entered value is accepted instead of the selection entry(S2). Step 2 can be omitted in this case, or consists in an instructionto load the last entered selection entry value from a memory.

Alternatively, the new IMSI_(w) calculated in step S4 (S41–S4 n) can bestored by the user temporarily in the RAM or E²PROM of subscriberidentity module SIM until the mobile unit is turned off or a new IMSIselected.

FIG. 4 shows by way of example a flow chart for the procedure of IMSIselection by entry of a PIN. In step S110 the selection program isstarted by entry of a new PIN. In step S11 an association for thecalculating rule in S12 is generated in accordance with the selectedPIN. This association defines which calculation rule is selected (notshown in the figure) or which identity value is added to originalidentity IMSI by means of a single calculating rule RV (step S12).

After execution of calculation rule S12, which consists in the simplestcase of the addition of an identity value to the original IMSI, the newidentity is outputted as described above for FIG. 3, step S5.

In the case of IMSI selection by means of a switch optionally having aplurality of switch positions, step S10 can be omitted since a newassociation can be determined directly from the switch position, forexample, or the switch position directly indicates this association.

The procedures shown in FIGS. 3 and 4 presuppose of course that forchecking entitlement to network access the IMSIs obtainable by thecalculation rules, i.e. the possible IMSIs, are either stored in themobile switching center or can be calculated there as in the subscriberidentity module, in which case the permissible identity values must bestored.

In the case of a new identity which was not approved when subscriberidentity module SIM was issued, the new identity values required forcalculating the new identity from the original IMSI can be inputtedeither directly by means of a terminal or using the OTA (over-the-air)function via the air interface.

FIG. 5 shows by way of example a menu displaying the possible identitieswith the corresponding identity values. The currently selected identityis indicated in the menu by emphasis, e.g. underlining. A new identitycan be selected for example by means of “forward keys” usually disposedin a mobile radio device and an “OK” function.

1. A mobile radio system having a plurality of mobile terminals (ME) connected with a mobile switching center (MZ) via an air interface for communication control and optionally for billing, the mobile terminals (ME) being controlled by a subscriber identity module (SIM) in which data for associating at least one user are stored, the subscriber identity module (SIM) having an initial international mobile subscriber identity (IMSI) associated therewith, wherein the subscriber identity module (SIM) contains a calculation rule for calculating and generating from the stored identity (IMSI) at least one new, additional international mobile subscriber identity (IMSI_(w)), the at least one new identity created by the calculation rule being associated accordingly in the mobile switching center (MZ).
 2. A mobile radio system according to claim 1, characterized in that the calculation or request for a new, additional identity (IMSI_(w)) is effected by a user entry via keyboard or menu.
 3. A mobile radio system according to claim 1, characterized in that the calculation or request for a new, additional identity (IMSI_(w)) is initialized by entry of a PIN.
 4. A mobile radio system according to claim 1, characterized in that a further directory entry and/or a further key are calculated together with the new, additional identity (IMSI_(w)).
 5. A method according to claim 4, characterized in that an identity is set by entry of a personal identification number (PIN) via menu and/or keyboard.
 6. A mobile radio system having a plurality of mobile terminals (ME) connected with a mobile switching center (MZ) via an air interface for communication control and optionally for billing, the mobile terminals (ME) being controlled by a subscriber identity module (SIM) in which data for associating at least one user are stored, the subscriber identity module (SIM) having an international mobile subscriber identity (IMSI) associated therewith, wherein the subscriber identity module (SIM) is configured to generate a request signal and in response to the request signal the mobile switching center (MZ) communicates a new additional international mobile subscriber identity (IMSI_(w)) associated with the subscriber identity module (SIM).
 7. A method for operating mobile terminals (ME) of a mobile radio system which are controlled by a subscriber identity module suitable for operation with an initial international mobile subscriber identity (IMSI) and at least international mobile subscriber identity (IMSI_(w)), wherein the at least one additional identity (IMSI_(w)) is created by a calculation rule from the initial identity (IMSI) stored in the subscriber identity module (SIM).
 8. A method according to claim 7, characterized in that the calculation is executed in the subscriber identity module (SIM).
 9. A method according to claim 7, characterized in that the calculation is performed in the mobile switching center (MZ) at the request of the mobile terminal (ME), and the new identity is communicated to the mobile terminal (ME) via the air interface of the mobile radio system.
 10. A method according to claim 7, characterized in that a further directory entry and/or a further key are calculated together with the new additional identity (IMSI_(w)).
 11. A method according to claim 7, characterized in that the new additional identity (IMSI_(w)) is newly calculated at each check or request by the mobile switching center (MZ) or the mobile terminal (ME).
 12. A method according to claim 7, characterized in that the new additional identity (IMSI_(w)) is stored temporarily in the subscriber identity module (SIM) until a new initial identity (IMSI) is selected or the mobile terminal (ME) is turned off.
 13. A subscriber identity module (SIM) for a mobile terminal (ME) in a mobile radio system in which an initial international mobile subscriber identity (IMSI) for a user is stored, wherein a calculation rule is stored in the subscriber identity module (SIM) for calculating from the initial identity (IMSI) at least one new additional international mobile subscriber identity (IMSI_(w)).
 14. A subscriber identity module (SIM) according to claim 13, characterized in that the subscriber identity module contains a temporary memory area (RAM) for temporarily storing a new additional identity (IMSI_(w)) which is calculated or communicated by the mobile switching center (MZ).
 15. A subscriber identity module according to claim 13, characterized in that a memory address pointer is provided for pointing to a selected temporary memory location where the current selected identity (IMSI, IMSI_(w)) is stored. 